Power converter for supplying electricity from a difference in temperature

ABSTRACT

An energy converting circuit, boosting the voltage supplied by a low direct voltage source, comprising a self-oscillating circuit, operating at very low voltage, using a voltage boosting transformer generating control signals of two chopper-boosters operating alternately. The circuit including an enhancement-type field effect translator used in synchronous switching with the self-oscillating circuit, which is in serial connection with an inductive resistor to the terminals of the source ( 1 ). The transistor being connected to a user circuit via a diode ( 15, 16 ). The circuit is used in a device for supplying electricity to appliances and by the production of thermal converters for the utilization of low-voltage thermoelectricity, as well as in a method for the manufacture of thermal converters on an industrial scale.

FIELD OF THE INVENTION

The present invention concerns an energy converter for feeding anautonomous apparatus with low consumption from thermocouples with a lowtemperature difference constituting a source of very low voltage and lowbut not nil internal resistance, the realization of the thermocouples,as well as an industrial manufacture process of the thermocouples.

BACKGROUND OF THE INVENTION

Many apparatuses have to function autonomously, that is to say that theycomprise their own power supply. It is the case of portable apparatusessuch as watches or auricular amplifiers which can not be permanentlyconnected to an electrical feeding system. It is also the case ofapparatuses placed in difficulty accessible places, such as intrusiondetectors used in alarm systems; they are placed for example in openingssuch as windows where it is difficult and expensive to bring a feedingcable.

These autonomous apparatuses with low consumption are currently fed bycells or rechargeable elements whose life or discharge duration islimited, what involves relatively frequent replacement or refilloperations and obliges to store piles or accumulators of replacement foravoiding an interruption of the functioning. One has already envisagedto exploit sources of very low voltage by using converters providing anoutput voltage in the order of some volts for feeding apparatuses withlow consumption reduced without interruption of functioning by using aself oscillating circuit comprising a step-up transformer and a fieldeffect transistor whose drain-source path is connected in the primary ofthe transformer.

These known converters are conceived for oscillating in such a way toincrease the voltage and they have a mediocre efficiency which does notallow to extract, from sources of very low voltage, the necessary powerfor the functioning of a watch or an auditive apparatus. Furthermore,the functioning of these oscillators is strongly disturbed when the loadbecomes significant; they can stop oscillating or even not start.

We know well documents: 1 (PETER WILSON “V Switching Mode PowerSupplies”), 2 (DE 14 37 235 A Philips), 3 (U.S. Pat. No. 3 679 918 AKEIZI), 4 (F. BUTLER “Transistor Inverter Frequency Stabilized CircuitSuitable for Running a Tape Recorder”, 5 (Patent Abstracts of JAPAN vol5, n°78 (E-058)), 7 (FR 1 162 168 A Soci{acute over (ete gene)}raled'équipement pour l'automobile, la locomotion aerienne).

All these documents comprise oscillator circuits, the diagrams describedin documents 3 and 7 are the closest to the invention, however none ofthem is able to spontaneously oscillate when the circuit is fed by adirect voltage as low as 10 to 200 millivolts. This is due to thethreshold effect occurring in the base-emitter junction of theoscillator transistor (in the order of 0.5 volt). A bipolar transistorhas to be polarized for being able to be used in a self oscillatingcircuit. This is not the case of the JFET transistor used in the presentinvention, it has a variable resistance when the gate-source voltage Vgsfluctuates around zero volt. The document 1 as well as the document 6(U.S. Pat. No. 3,913,000 A GILBERT, CARDWELL) show converter circuitsusing the load of an inductance for converting a voltage, the process iswell known as stated in the document 6, FIG. 1. What is new in theframework of the present invention is the association of theself-oscillating circuit and of the chopping converter which isoptimized for the very low powers (10 microwatts to 10 milliwatts),without other source of energy for the operation of the converter.

SUMMARY OF THE INVENTION

The basic problem solved by the invention is to provide an energyconverting circuit having an efficiency allowing one to extract thedesired power and voltage from sources of electrical power of very lowvoltage and whose functioning is insured even for a significant load.For this purpose, the object of the invention is an energy convertingcircuit which boosts the voltage provided by a source at low directvoltage with small internal resistance, comprising a self-oscillatingcircuit, functioning at a very low voltage, using a voltage step-uptransformer generating the control signals of two chopper-step-uptransformers with alternate operation, of the type comprising anenhancement mode field effect transistor which is used as a synchronousswitch with the self-oscillating circuit, which is connected in serieswith an inductance to the terminals of said source and which isconnected to the user circuit through a diode.

The use of chopper-step-up circuits allows to extract approximately 50%of the available power in the source. One can feed apparatuses with avoltage of some volts from a source whose voltage is in the order ofsome tens of millivolts.

Moreover, the functioning is insured for important loads.

Advantageously, a voltage limiting diode and a condenser of greatcapacity or an accumulator is connected to the output terminals.

In this manner, the output voltage is determined to the desired value.

The invention has also for object a reversible converter circuit,characterized in that it comprises two converter circuits which areantiparallel connected to the source and bound to the output terminalsthrough four switches which are controlled two by two by twosupplementary windings of the transformer of the operating converter andin that each converter comprises a blocking device blocking the otherconverter when it is operating.

Such circuit allows to extract energy provided by a source whosepolarity is variable. The two converters operate alternatively accordingto the polarity of the source, the operating converter blocking theother converter for avoiding any power loss in the non operatingconverter.

Advantageously, the blocking device comprises a third supplementarywinding of the transformer to whose terminals is connected a rectifiercircuit generating a direct voltage blocking the self-oscillatingcircuit of the non operating converter.

The invention had also for object a device for feeding an autonomousportable apparatus from a thermal system comprising a hot source and acold source with a low temperature difference between them, such as theepidermis of a human being and the ambient atmosphere, characterized inthat it is constituted by a converter circuit in which the electricalsource is constituted by an assembly of Seebeck effect detectorsconnected between the two thermal sources. This converter is alsosuitable for extracting the power of photovoltaic source.

Such a feeding device can be integrated in a watch or an auditiveapparatus. It can also be used for recharging a rechargeable element.

BRIEF DESCRIPTION OF THE DRAWINGS

Others characteristics and advantages of the invention will appear fromthe following specification, which is illustrative and not at allrestrictive, by referring to the joined drawings on which:

FIG. 1 is the diagram of a converter circuit according to the invention;

FIG. 2 is the diagram of a reversible converter circuit according to theinvention,

FIGS. 3a-3 f are diagrams of functioning of the converter circuit of theFIG. 1;

FIG. 4 represents a feeding device from a source of energy of thermalorigin;

FIG. 5 illustrates the use of a feeding device from a source of energyof thermal origin placed on a wall;

FIG. 6 illustrates the use of a feeding device from a source of energyof thermal origin placed on the ground;

FIG. 7 illustrates the use of a feeding device from a source of energyof thermal origin placed on a pane;

FIG. 8 represents a feeding device according to the invention used inreplacement of the cell of a watch;

FIG. 9 represents another watch originally equipped with a feedingdevice according to the invention;

FIG. 10 represents again another mode of realization of a watchaccording to the invention;

FIG. 11 is the electrical diagram of the watch of the FIG. 10; and

FIG. 12 represents a shoe equipped with a feeding device according tothe invention;

FIGS. 13 is a prspective view of bars of N and P material, respectively;

FIG. 14 is a perspective view showing bars of N and P material alignedand interlaced in an alternating array;

FIG. 15 is a side view of bars joined by tracks;

FIG. 16 is a top view showing an element made of bars in a bentconfiguration;

FIG. 17 is a side view of an arrangement showing the rod made of barsglued to a support;

FIG. 18 is a perspective view of a another arrangement showing a rod ofbars covered by a distribution barrier;

FIG. 19 is a schematic of a cooling system;

FIGS. 20a, 20 b and 20 c are views of a microgenerator in the form ofbracelet link;

FIG. 21 is a perspective view showing alternating slices of P and Nmaterial;

FIG. 22 is a perspective view showing ingots of material alternatingbetween P and N material;

FIG. 23 is a perspective view showing the ingots sliced into sections ofbars, and

FIG. 24 is a perspective view of a section of a thermoelement accordingto the present invention.

FIG. 1 is the diagram of a converter circuit intended for extracting theelectrical power provided by a source 1 of very low voltage, for exampleof 10 to 200 mV, that has a minimal internal resistance schematized by2, providing a much more high voltage, for example a voltage of 2 V foran electronic apparatus. The electrical source 1 is connected on theprimary 3 of a step-up transformer 4 by the in termediary of thesource-drain path of a n-channel field effect transistor (JFET) 5. TheJFET transistor 5 is of the pinch effect type, that is to say that, fora nil gate voltage, its drain source resistance is not infinite but inthe order of some ohms and its is pinched when the gate voltage becomesnegative.

The secondary of the transformer 4 comprises two similar windings 6 and6′ connected by a mid-point 7 connected to the ground. The gate of theJFET transistor 5 is connected to the ground by a resistance 8 and thesecondary 6′ by a condenser 9.

When the gate voltage varies, that involves a variation of thedrain-source resistance and, as a result, a variation of the current inthe primary 3 which creates a high voltage on the secondary 6′ of thetransformer 4. The frequency of this oscillation depends on theinductance of the transformer 4, the distributed capacity of thesecondary 6 and 6′ and the gate-source capacity of the JFET transistor5. The condenser 9 realizes a galvanic decoupling of the gate and allowsthe oscillator to consume very few energy, due to the P N gate-sourcejunction.

In accordance with the invention, one uses, for each half-wave of theoscillation, a circuit of the type chopper-step-up transformercomprising transistors 11 and 12 of the n-channel enhancement modeMOS-FET type, whose gate-source voltage threshold is low (for example, 1to 3 V), an inductance 13, respectively 14, and a Schottky diode 15,respectively 16. Each MOS-FET transistor 11, respectively 12, isconnected in series with the inductance 13, respectively 14, and theirgates are controlled by the secondary 6′, respectively 6 of thetransformer 4 whose outputs are crossed in such a way that the gatevoltages of both MOS-FET transistors 11 and 12 are in opposition ofphase.

Each Schottky diode 15 and 16 is connected between the drain of theMOS-FET transistor and the positive output pole. A condenser 17 of veryhigh capacity and a voltage limiting diode I are in parallel on theoutput terminals of the converter.

Both these elements are used for determining the value of the outputvoltage; they can be replaced by a rechargeable element.

The functioning of this converter circuit is illustrated by the diagramsof FIGS. 3a to 3 f which represent respectively the voltages of thesecondary 6 and 6′, the current in one of the inductance's, thedrain-source voltage of one of the transistors, the current in the otherinductance, the drain-source voltage of the other transistor and thevoltage of the source 1. When the gate voltage of the transistor 12 ispositive and higher than the threshold, Vs, this transistor isconducting, the inductance 14 progressively accumulates energy as longas the circulating current increases while the voltage on the terminalsof the source 1 decreases in a quasi linear manner. When the gatevoltage decreases back under the threshold, the transistor 12 is blockedand the energy stored in the inductance 14 is transferred to thepositive output terminal by the diode 16. For the next half wave, thetransistor 11 loads the inductance 13 that unloads then on the output.

The advantage of the use of the two chopper-step-up-transformers is thatthe self-oscillator is, from the energy standpoint, used in its singlefunction of oscillator and that the available alternative voltage isonly used for monitoring the chopper-step-up-transformers. FIG. 2represents a reversible converter that can extract energy provided by asource 21 of very low voltage whose polarity varies. Two convertercircuits are antiparallel connected on this source in such a manner tobe alternately operating in dependence of the polarity of the source 21.Each of these circuits comprises a JFET transistor 22, respectively 22′,a primary 23, respectively 23′, a secondary with double winding 20 and24, respectively 20′ and 24′, two MOS-FET transistors 25 and 26,respectively 25′ and 26′, two inductance's 27 and 28, respectively 27′and 28′, and two Schottky diodes 29 and 31, respectively 29′ and 31′which are connected on the output 32 by the intermediary of switchesthat will be described hereunder.

The transformer of each converter comprises a supplementary winding 33,respectively 33′, whose voltage is sent on a rectifier circuitconstituted of two diodes 34, respectively 34′, associated with acondenser 35, respectively 35′, and whose direct output voltage isapplied between the source and the gate of the JFET transistor 22′,respectively 22 of the self-oscillating circuit of the other converterin such a way to insure the blocking of the second converter while thefirst is operating and conversely.

The output voltage of each chopper-step-up transformer is sent on theoutput terminals, U+ and U−, by the four intermediary switches 39, 41,38 and 37, MOS-FET transistors, which are connected as a bridge circuitand which are each controlled by the voltage coming from thesupplementary windings 42 and 43, respectively 42′ and 43′, of thetransformer of each converter transformer which is rectified by thediodes 44 and 45, respectively 44′ and 45′, and filtered by condensers.

When the voltage supplied by the source 21 is positive, it is theself-oscillating circuit comprising the JFET transistor 22 thatoscillates. As a result, it supplies a direct voltage which insures theconduction of MOS-FET transistor switches 41 and 39. The positiveterminal of the chopper-step-up transformer (cathode of the diodes 29and 31) is thus switched via the drain-source path of the MOS-FETtransistor 41 on the output U+. The negative output of thechopper-step-up transformer (sources of transistors 22, 25 and 26) isthus switched via the source-drain path of the MOS-FET transistor 39 tothe output U−.

Furthermore, the winding 33 supplies a voltage which, once rectified bythe diodes 34 and filtered by the condenser 35, is going to block theJFET transistor 22′ of the non-operating self-oscillating circuit whosedrain-source resistance was low till that time.

When the voltage delivered by the source 21 is negative, theself-oscillating circuit comprising the JFET transistor 22′ isoscillating. The operation is identical to the operation describedabove. The MOS-FET transistor 38 is going to switch the positive outputof the chopper-step-up transformer (cathodes of the diodes 29′ and 31′)on the output U+. The MOS-FET transistor switch 37 is going to switchthe negative output of the chopper-step-up transformer (sources oftransistors 22′, 25′ and 26′) on the output U−.

Similarly, a negative voltage supplied by the rectification of thevoltage of the secondary 33′ is going to block the JFET transistor 22.

The winding 20, respectively 20′, constitutes an alternative of thewinding 6′ of the circuit of the FIG. 1. It allows to operate theself-oscillating circuit with the right winding ratio and allows toincrease the control voltage of the MOS-FET transistors of thechopperstep-up transformer for obtaining more clear switches.

According to the mode of realization of the invention, the source of lowvoltage energy is constituted by an assembly of effect Seebeck detectorsplaced between a hot thermal source and a cold thermal source whosetemperature difference is low, for example some degrees. These twosources can be constituted by the epidermis of the person using anautonomous apparatus and the ambient atmosphere.

FIG. 4 illustrates the principle of such a feeding device using heat ofanimal origin. It comprises a substrate 51 in thermally insulatingmaterial in which are placed Seebeck effect detectors 52, in the form ofsmall bars, that is to say of the thermocouple type. Considering the lowvalue of the voltage delivered by such detectors, namely 0.2 mV byCelsius degree (Seebeck coefficient), they are connected in series forobtaining a voltage of 10 to 200 mV. All bars are placed between acollector plate 56 placed directly on the skin 53 of the user and anintersection of heat 54 exchanging the heat with the ambient air. Twoelectrodes 55 provide the low output voltage for the converter.

FIG. 5 illustrates the use of a source of thermal origin between the twosides of a wall 61. The Seebeck detectors are placed between a radiator62 placed inside the room and constituting a heat exchanger with theinternal air and an exchanger 63 with the external air which comprises apost 64 crossing the wall 61 in section 65 in thermally insulatingmaterial.

FIG. 6 illustrates the case where one uses the temperature differencewith the ground 71. A thermally insulating support 72 is placed in theground and it comprises a heat exchanger 73 at its upper part. TheSeebeck detectors are placed between the lower face of this heatexchanger 73 and the upper face of a thermal collector stake 74 plantedin the ground.

This feeding device uses a reversible converter because the temperaturedifference between the ground and the ambient air is reversed betweenday and night. This feeding device can for example be used in the domainof the ground road signs. Especially, one can use it to feed a luminousdevice 75 such as a light emitting diode and to realize a signaled whiteline.

FIG. 7 represents the use of the temperature difference between the twofaces of a pane 81. One employs an heat exchanger 82 placed on theexternal wall of the pane in contact with the external air, a collectorplate 83 placed on the internal face of the pane and a heat exchanger 85placed on a thermally insulating support 84 placed on the internal faceof the pane and receiving the collector plate 83. The Seebeck detectorsare placed between the collector plate 83 and the heat exchanger 85.

The feeding device of FIGS. 5 and 7 can for example be used for feedingan intrusion detector placed in the vicinity of an opening of abuilding, such as a window and autonomously operating.

FIG. 8 is a cross-section of a watch 91 which comprises, in the bottomof its casing, a cell receptacle 92. A feeding device according to theinvention is inserted between the skin of the user and the bottom of thecasing instead of the primitive closing cap of the watch. It comprises aheat collector bottom 93 on which the Seebeck detectors 94 are placedalong a circle by being embedded in a thermally insulating material 95.A receptacle 96 in the form of a cell comprises the electronic circuitsand is placed in the cell receptacle 92.

FIG. 9 represents a watch in which the feeding device is integrated inthe casing. In this case again, the Seebeck detectors 101 are placedalong a ring and the electronic circuit are contained in the body 102 ofthe watch and embedded in a thermally insulating material 103.

FIG. 10 represents a mode of realization of a watch in which, forincreasing the exchange surface and, as a result, the power of thesource, the Seebeck detectors are placed in the bracelet of the watchwhich is constituted of articulated links in which are place Seebeckdetectors. In this case, a photovoltaic generator 111 is attached on oneof the links; it can be directly connected in parallel on the output ofthe feeding device according to the invention or comprise also aconverter circuit. The FIG. 11 indicates the electrical diagram of thetotality, the sources constituted by each link being connected in seriesfor constituting the electrical source connected to the converter.

FIG. 12 represents the integration of a feeding device according to theinvention in an footwear such as a shoe. In this case, the Seebeckdetectors 121 are lodged in the sole 122 of the shoe and use thetemperature difference between the user's foot and the ground. It isprovided with a feet heat exhausting plate 123 which is in contact withthe Seebeck detectors as well as a plate 126 collecting the heat of thefeet. The electronic circuits 124 are also lodged in the sole 122.

The feeding device can be used for feeding safety devices such as lightemitting diodes 125.

In the case of a ski boot, the feeding device can activate a transmitteror a transponder w which allows one to find the user in case of accidentsuch as an avalanche or feed by contact the electronic d devicereleasing the release binding.

The above description of examples of realization of the invention hasbeen provided only for illustrative and not at all restrictive purposeand one can bring there modifications or alternatives withouttrespassing the scope of the present invention. Especially, one can useothers sources at very low voltage or use several ones in combination.

The reversible converter of FIG. 2 can be used in the case of heatexchanges with the ambient air, for example in the case of FIGS. 5 to 7.This reversible converter allows to provide a feeding when thetemperature difference, for example between the earth and the ambientair, is reversed between day and night. One recuperates all possibleenergy by using the flowing and the flowing back of the heat exchanges.

Furthermore, one can realize an auricular amplifier fed by a feedingdevice using the temperature difference between the skin and the ambientair and placed in or around the ear.

Such an energy converter efficiently takes advantage of the very lowvoltages generated at a low impedance by a thermoelectric module usingthe Seebeck effect, when the later is submitted to a low temperaturedifference.

It also efficiently takes advantage of the very low voltages generatedat a low impedance by a thermoelectric module using the Seebeck effectcomprising only some pairs, when the latter is submitted to a hightemperature difference.

Such a thermocouple, for example constituted in N and P doped FeSi₂,tolerant temperature differences of approximately 700° C., a unique pairgenerates then between 100 mV and 1 V.

A unique pair can for example contribute to feed a thermometer formeasuring high temperatures with an autonomous sensor. The action of theconverter at the output of the thermocouple regulates the feedingvoltage of the thermometer, the thermometer can for example use thevoltage of the thermocouple for measuring the temperature.

A first example of realization of a thermocouple in iron disilicideconcerns the measure of the temperature of a food container, a pan, apressure cooker or a stove for example.

The generation of energy is realized by the FeSi₂ device insertedbetween the wall of the container, which is heated during the cooking,and the sleeve, which acting as a radiator. The converter at the outputof thermocouple generates the operating voltage of the thermometer.

This example can also be realized with a thermocouple module withbismuth tellurium such as described in the second part of thespecification, instead of the FeSi₂ device, since the hot temperaturedoes not exceed 250° C.

A second example of realization concerns the safety of gas ring, whoseself-extinction is to the cause of many accidents.

A piezoelectric lighting device is provided for automatically relightingthe accidentally blown flame. A couple in FeSi₂ a junction of which isin the flame and the other at the temperature of the water of the waterdelivery pipe constitutes an excellent way for the electrical feeding ofthe lighting device. The converter circuit makes its functioning secureand simplifies the installation.

A third example of application concerns the electrical generation of acar.

Traditionally ensured by an alternator, the recharge of the battery andthe supply of the electrical power are made to the detriment of thepropulsion. Nevertheless the thermal engine dissipates much heat whichis lost in the environment.

This heat can be converted in electricity at a voltage of 12V by athermoelectric process. A FeSi₂ thermocouple in contact with the exhaustand in contact with the water circuit observes a temperature differencebetween its faces which can reach 700° C.

A couple is sufficient for generating a usable voltage by the abovedescribed converter circuit. A high power version of this circuit wouldbe recommended.

The economy of fuel resulting such a process can reach 20%.

One describes hereafter a mode of realization of a thermocouple modulewhich is used for the low temperature differences, based on bismuthtellurium.

The thermocouples called Peltier or Seebeck effect elements arecurrently used in the industry for the cooling.

When it is fed by a current, the thermocouple absorbs the heat on one orits faces and rejects it on the other. Operating as a heat pump withoutmobile part, this device is remarkable by its integration and itsreliability more than for its energy efficiency and its manufacturecost.

Submitted to a temperature difference between its collector faces, andenergized by a thermal flow, the thermocouple acts as an electricalgenerator with low impedance, it transforms a part of the thermal flowin usable electrical power. Here also, the generator has a remarkablesimplicity but deplores a bad efficiency and a disputable economicprofitability.

Thermoelectric modules are traditionally constituted of an electricalcircuit including alternately N and P doped semiconducting barsconnected in series, these bars undergo in parallel the thermal flowcrossing the module.

Traditionally, these vertical bars are aligned in compact ranks in ahorizontal plane and sandwiched between two ceramic insulating plateswhich are supplied with a screen process printed electrical circuit.

A general characteristic of this type of realization is the low electricimpedance of the module, direct consequence of the limited number of lowelectrical resistance bars. It results either the necessity of a lowvoltage feeding for the generation of cold or the use of a step-upvoltage converter at the output of the thermocouple generator.

A second characteristic concerns the difficulty of the integration or ofthe mounting of this module in a thermal system: since the thermal flowdoes not cross the interstices, the module has to be glued, compressedor soldered to its thermal drains, this requires precision and to knowhow and this involves efficiency losses. The modules are in generalrealized in ceramic, for securing the electric insulation of the circuitand the good conduction of the thermal flow and for avoiding the ruptureentailed by dilatation's associated with temperature differences betweentheir faces. It is not possible to solder these modules, the gluing isdelicate and the compression necessitates dissipator fittings. Moreover,the thermal drains on which the modules are mounted must have highconductivities or significant dissipations because of the intensity ofthe flow which crosses the module.

A third characteristic of modules concerns their sensitivity to thecorrosion. Indeed, semiconducting bars are generally mounted withoutprotection, so as to limit the thermal losses, they are then exposed tothe corrosion.

Finally, the critical characteristic of these modules is their cost.

The cost factors are successively: the price of the thermoelectric rawmaterial, the cost of the transformation, the cost of the cutting inelements,

the handling of the miniature elements, the cost of the ceramicmaterial, its cutting, of its serigraphy and of the soldering andfinally the cost of the mounting, of the pressing and of the burning ofthe module.

The invention presents a thermoelectric module which improves the fourgeneral characteristics, a process of realization of such modules aswell as some examples of applications.

According to the invention, the thermocouples are realized fromsemiconducting materials with N and P type carriers, electricallyconnected in series and thermally connected in parallel.

Materials of types P are for example realized from an alloy containing acomposition of 77.5% of Sb₂ Te₃ in 22.5% of Bi₂Te₃ m materials of type Nare realized from an alloy comprising 5% Bi₂Se₃ in 95% of Bi₂Te₃.

According to the invention each material undergoes a vacuum annealing ata temperature of 650° C. during a duration of approximately 12 hours,under a quartz bulb, then a crystallization at a controlled temperatureaccording to the method named THM (Traveling Heater Method), generatinga bar of diameter in the order of 30 mm at a speed of approximately 20mm per day. By this method, it is possible to obtain polycrystal mmaterials of high thermoelectric quality, whose coefficient of merit Zin the order of 3×10⁻³ K⁻¹ exceeds that of materials commercializedtoday (Z=2.5×10⁻³ K⁻¹ approximately). Such a material increases theefficiency coefficient of a cooling device by approximately 30% withregard to materials used today. It has an axis A of best efficiency asshown by the axes A of bar materials 201 and 202 of FIG. 13 showing barsof “N” and “P” materials, respectively.

According to the invention, the bar materials are cut into bars 221 and222 of P and N, mounted and wrapped.

According to a preferred, but not exclusive, mode of realization (FIG.14), the elementary thermocouple is constituted by a same number of Ndoped bars 221 and of P doped bars 222 aligned and interleaved to form arod 220. These bars 221 and 222 have the same dimensions, for examplewith a squared basis of width L between 0.45×0.45 and 1×1 mm and heightH between 1 and 3 mm. The number of bars 221 and 222 will vary infunction of the applications between 20 and 400 approximately.

According to the invention, the aligned bars alternately N (221) and P(222) are glued one to the other on their opposite faces. Such a gluingwill be realized for example by insertion between each bar of a membrane223 preimpregnated for a fusible printing or interlining, whose adhesionis insured during a cycle of hot compression.

A Kapton film of low thickness, approximately 25 microns, preimpregnatedon a total thickness of 75 microns realizes a durable and solid bridgingbetween each bar, by insuring the electric insulation between them.

The Kapton film, whose thermal conductivity is 10 times lower than thethermoelectric material, entails only a very low thermal bridge betweenthe bars, its influence on the performances is negligible. Moreover theKapton is a strengthened material, compatible with the epoxy gluing. Itconsolidates the structure by protecting the bars.

A membrane in glass fibers preimpregnated with epoxy is alsoappropriate.

According to the invention, aligned bars are wrapped on their sides by alow thickness membrane 224. The latter is glued on its sides, adheres tobars and to the intermediate membranes. These membranes finishconsolidating the alignment, protect each bar whose sections 225 onlyremain apparent.

Such a membrane is for example realized from a glass fibers weavingpreimpregnated with epoxy resin or with a Kapton film primpregnated inan epoxy resin.

The Kapton has the advantage of a preslashing only on a single face. Thefusible printing for interlining under pressure consolidates andstrengthens the structure.

The epoxy glass will be preferred for allowing a formatting of theelement before the thermosetting. It appears possible to bend the rod220 and to give it the indispensable curvature for some mountings. Sucha form represented in plan view in FIG. 16 will be imposed beforeburning, which will coagulate it definitively.

According to the invention, the bars 221 and 222 are electricallyconnected in series, N P junctions between two successive bars beingrealized on the upper sections superior, P N junctions on the lowersections.

According to the first mode of realization of the invention, junctionsare realized directly on the section of bars, by tracks in nickel231FIG. 15 with a thickness of the order of 50 microns approximately.Each joining element has a length slightly inferior to 2×L and a widthof L, it insures the junction by totally covering totally the sectionsurface of two successive bars. According to several examples ofrealization that will be detailed in the description of the process ofmanufacture, the section is either covered with a layer of chemicalnickel with a thickness of 50 microns, sectioned at the appropriateplaces, or covered with a very thick fastening layer in nickel, on whichthe track of nickel is tin bismuth 232 soldered, or the section isetched with acid, what only protects the bismuth, which is bismuthsoldered with the nickel track.

By this first mode of realization, the electrical circuit in nickel isdirectly deposited on the sections, what contributes to the protectionof the material because the nickel constitutes an excellent chemicalbarrier and oxidizes only a little.

In this first mode of realization, the rod will be preferentially gluedto the thermal drains 251 of FIG. 17 during the mounting, according tothe usual processes in electronics for dissipating the heat ofcomponents towards the circuit on which they rest.

Such a gluing insures an electrical insulation between the component andthe support for example metallic and electrically conducting, thisquality is indispensable in order that the nickel tracks are notshort-circuited. Such a gluing insures a good conduction of the heat tothe support because of the intrinsic thermal conductivity of the resin252 optimized for this application. A good resin presents a conductivityequivalent to that of the thermoelectric material. Finally, themechanical stability of such a gluing can be optimized by areinforcement in glass fibers in the resin, insuring a secured strainrecovery. An epoxy glue loaded with a conducting ceramic impregnating afine fiber weaving realizes an optimization of the mechanical stability.Such a gluing realized hot under pressure fixes the rod on the supportwith a robust anchorage. Since the epoxy resin of the thermal glue meltswith the epoxy resin of the membranes, the structure is strengthened andbars are then totally wrapped.

According to a second mode of realization in FIG. 18, sections of bars221 and 222 are covered with a very fine layer of nickel acting as adistribution barrier. The rod 220 is secured with tin bismuth 263 brazedon a printed circuit 261 that realizes the joining of the bars bycontiguous parallel tracks 262 which are isolated one against the otherand spaced by the 2L pitch and whose width is slightly inferior to 2L.These rectangular tracks 262 have a some millimeter length, they are innickel-plated copper. In this second mode of realization, the printedcircuit is formed from a thin “flex” type membrane 264 constituted by aglass fibers weaving impregnated with an epoxy resin loaded with heatconducting elements, such as a ceramic powder, covered with a coppersheet 262 of usual thickness, 35 or 70 microns. It will be taken care torealize an engraving of the copper circuit, then a nickel deposit asscattering barrier, and finally a bismuth pre-tinning.

An example of realization implements a pre-laminated epoxy glass loadedwith boron nitride glued on a copper strip. The serigraphy and theengraving of the copper define the circuit, it is then brazed afternickel-plating on the bars.

In this second mode of realization, the printed circuit is glued onmetallic pieces acting as thermal drains 265, in aluminum, copper, tin,sheet steel, nickel steel, invar or stainless steel according to theapplication, or the circuit is integrated, to a classic circuit providedwith copper plane dissipators and for example with coppered passages forthe heat transfer.

Printed circuits of the stratified type copper on aluminum suitparticularly to the application, after nickel-plating of the copper.

In this mode of realization, the rod is sandwiched between two suchcircuits and hot pressed for consolidating both the soldering and theepoxy glue.

It has been described two examples of realization of the elementarythermocouple elementary in the form of a rod constituted by a row ofalternately N and P doped bars. In one case, the electrical circuit isrealized in nickel on the rod supplied with connectors at itsextremities, in the other case, the circuit is realized on the support,under the form of a printed circuit, on which is the rod is brazed.

In both cases, the rod is hot pressed preferably between the supportacting as a lower thermal drain and the upper thermal drain.

A cold pressing with a polymerizable thermal glue is also possible.

Another example of realization of the module is constituted by multipleattached rods for constituting a block whose dimensions are in the orderof 10×10×2 mm³. Its constitution is the same, its characteristics aresimilar.

According to the invention, the elementary component presents elementarycharacteristics of electrical impedance, thermal, power of cold, as wellas useful section corresponding to the section of its basis.

The modes of mounting of these elementary thermocouples rods facilitatetheir integration in thermoelectric cooling systems or thermoelectricgenerators, because it allows to match the density and the number ofelementary modules with the thermal and electrical characteristics ofthe interfaces.

Especially, an usual thermocouple presents a significant thermalconductivity, and potentially and important flow, entailing sometimesthe necessity to dissipate heat and cold by large finned radiators andin forced state.

A lesser thermoelectric matter density allows the example to distributethe thermocouples with a lesser cost on an important surface and,therefore, to have larger exchange surfaces without ventilation orcumbersome fins. That simplifies the transportation of the heat. By thisprocess, hot and cold faces can be only very simple single aluminumplates isolated one against the other by a self adhesive foam placedaround the components.

In the thermogeneration, the temperature differences are reduced, thedissipated powers are weak, as well as the densities of rod.

According to the invention, we describe a first example of realizationof a cooling device for example destined for a mini-refrigerator.

Such a device comprises an internal cold face, an external hot face,and, optionally, of a heat exchanger.

Depending of the performances, the hot external face dissipatesapproximately twice the heat drawn in the cold part. Thereforesometimes, there is provided an artificial ventilation whose principleis described hereafter.

The cold face 271 of FIG. 19 constitutes the structure of the coolingsystem. It is realized from of a laminated printed circuit nickel-platedcopper on aluminium. On the aluminium is laminated a sandwichconstituted of a glass fibers layer preimpregnated to the thermalconducting resin, and of a copper layer copper forming the desiredelectrical circuit 272.

The electrical circuit is distributed in two zones:

A first zone in which the feeding and regulation device is implanted, asecond zone forming the thermoelectric circuit.

The feeding and regulation circuit is realized from components tomounted in the surface, implanted in the first zone. It is constitutedof a simple diode rectifier, of a condenser 274 and of a multiple relay275 controlled by the integrated thermostat 276.

The thermocouple rods 277 are soldered with tin bismuth and implanted inthe zone of the thermoelectric circuit, according to a series-paralleldiagram. The mounting process is in accordance with the standards of theCMS components.

A layer of thermal adhesive foam 278 fulfills all the residual volumebetween the components, on a height of in the order of L.

Finally, a mosaic of thermal dissipators 279 are covering the zone ofthe thermocouple rods, each dissipator supplied with a laminatedcopper-tin circuit is soldered on between from 2 to 4 rods, and forexample consolidated in its center by a stainless steel rivet.

These dissipators 279 are for example realized in extruded aluminum.

According to a not exclusive mode of realization of the invention, anoptional ventilator 701 realizes a forced dissipation in a tunnel 702around the blades of the dissipators. This ventilator is released inparallel with the thermocouples, under the control of the thermostat.Associated with the tunnel of ventilation and the ventilator, two valves703 seal, under the effect of their mass, the entries and exits of thetunnel, so as to reduce to the maximum the effect of insulation losswhen the relay is opened, consequence of the thermal conductivity of thecells. These valves open just at the activation of the ventilator andthe thermocouples.

An insulating wall 702 and 278 contributes to strengthen the insulation,particularly around the tunnel of ventilation.

Such a process is usable for mini-refrigerators, for mini-airconditioners, for cooling systems of industrial or food liquids, (inthis particular case, the cold wall 271 is in contact with a fluid heatexchanger), for stalls of butchery, etc.

This device optimizes the bulkiness and the cooling efficiency, as wellas the insulation. Indeed: it presents a great exchange surface for thecold face, therefore it authorizes an only convective exchange withoutventilator and without bulkiness, it concentrates moderately the flow onthe hot face, and it is possible to condition, during the functioning ofthe thermocouples, the thermal exchange with the outside by forcedventilation.

Moreover, the feeding circuit is implanted in a surface that is lost forthe cooling without further expense.

For an application of this type, one will prefer square modules of about10×10 mm ² constituted of joined rods, each pumping approximately I watton a surface of 10 cm².

According to the invention, we describe on FIG. 20 an example ofelectrical microgenerator in the form of a link of bracelet.

The heat collect is realized in laminated aluminum copper 281 whosecopper 282 is nickel-plated or in printed circuit.

The dissipator is realized in laminated aluminum copper 283 whose copper284 is nickel -plated. This dissipator represents the upper face of thebracelet and comprises small fins 285.

On both sides of the link, as well as on the central zone, rods of about10 mm of length are brazed between the collector and the dissipator. Ateach end of the link, a nickel-plated pivot 287 is brazed on theinternal face of the dissipator or on the internal face of thecollector, it insures the electrical continuity from link to link thanksto a conducting axle.

A rivet or a stainless steel screw contributes to consolidate the linkby exerting a pressure on the brazing.

A foam (not shown) insures the protection and the cleanness of the link,as well as the insulation between the two faces.

At the wrist, the temperature difference between the collector and thedissipator induces a thermal flow which is converted intoback-electromotive force collected between the pivots.

With approximately 20 pairs N P per link and a temperature difference inthe order of 10° C. between the faces, each link with a surface of 2 cm²generates a potential difference of the order of 20 mV, under animpedance of 2.4 ohms, i.e. approximately 80 microwatts maximumdelivered.

This constitutes a not exclusive example of implementation of optimizedthermogenerator. The output voltage is proportional to the difference oftemperature between collector faces and dissipator faces and to thenumber of N P couples, and, moreover, the delivered electrical power ismaximum when the thermal resistance of the bars is equivalent to that ofthe dissipator, the total section of the authorized thermoelectricmatter is therefore determinated. The maximum voltage is obtained forbars whose ratio H/L² is maximum.

For a low section and great length the bars are fragile, and thereinforcement by membranes contributes to render the optimization thefactor H/++L2 possible.

These two implementations of elementary modules in the form of rods arenot limitative and the given examples develop their simplicity.

According to the invention, we describe a process of realization of arod module.

Each rod contains an alternation of P and N doped thermoelectricmaterials. These materials undergo a crystalline growth and present ananisotropy axis A FIG. 13 of the thermal conductivity and of the factorof merit.

According to the invention, original N and P ingots are rectangular,elongated along the anisotropy axis.

Ingots are then cut in parallel slices containing the anisotropy axis,with a thickness close to L. Such a cutting is for example realized witha multiple disk circular saw or with a disk saw.

The slices 291, 292 of FIG. 21 are then alternated P and N bymaintaining parallel axes, superposed, by inserting in each slice athermo-adhesive membrane 293 of low thickness. This membrane is forexample a Kapton of 25 micron comprising on both sides 25 micron ofepoxy resin, or well an epoxy glass.

The reconstituted ingot is therefore a composite constituted of analternation of a N P electrically isolated slices.

A first burning insures a partial polymerization, under pressure, attemperature close to 130° C.

After processing, the new ingot is then cut again in slices ofapproximately L thickness according to planes containing the anisotropyaxis and perpendicular to the preceding slices.

Each slice 2101 of FIG. 22 containing rectangular stems of section L²alternately in N and P material is then covered on both sides by twomembranes in Kapton 2102, 2103 pre-glued only on one face. The slicesare then superposed and the ingot reconstituted. One realizes thus rods,because slices are not glued one to the other. It is also possible tocover slices with epoxy glass, and to separate them by a strippingmembrane in pacothane. The latter will authorize the separation of therods.

Finally, for realizing module blocks, one will insert between the slicesonly one membrane in Kapton pre glued on its two faces or a membrane inepoxy glass. One will take care to alternate the N and P bars forobtaining a checked distribution.

A cycle of burning under the pressure finished the polymerization of theslices.

The ingot is then cut according to the perpendicular plan to theanisotrophy axis in slices of thickness H, 2111, 2112, FIG. 23, eachslices showing the sections of the bars.

Each slice contains the elementary N P rods, the rods are juxtaposed andare linked by the residual adherence. A shearing dissociates them.

The modules remain in block.

The slice of FIG. 24 presents the sharp sections of the thermoelements,it is protected by a deposit of nickel, electrochemical or chemical, ina bath. The nickel acts as a distribution barrier and adhesive interfacefor the brazing.

Several alternatives appear.

The deposited nickel layer has a high thickness, approximately 0.1 mmand it insures a continuous recovery of the slice, with robust fasteningof the bars. Then, by cutting or selective chemical etching, it ispossible to realize directly the connections between the bars, then toseparate the rods supplied with their proper electrical circuit. A flashby sputtering contributes to release the fastening before the chemicaldeposit. The bar is destined to be glued with the thermal glue.

The layer of nickel has a low thickness, as is seen in FIG. 24. Theslice 2120 is nickel-plated on the section of bars exclusively. Then itis possible to braze under hot press a flexible circuit in copper tinbismuth 2121 pre-welded on a membrane in epoxy glass loaded with boronnitride. A phase of pressing at the temperature of brazing of the slicesolders the junctions. The circuit will have been preliminary engravedby serigraphy on the copper bound with an adhesive transparent leaf 2122in loaded epoxy glass. Each rod realized by this process comprises twoweldable strips, the rods are separated by cutting of the membrane inloaded epoxy glass.

The layer of nickel is fine, the rod is destined to be welded on aprinted circuit that insures the junctions between the elements. Theprinted circuit is in nickel-plated copper bismuth. A stratifiednickel-plated copper-aluminum constitutes the best technicalalternative.

It has been described a thermoelectric module under the form of amulti-element rod, mounting version of this rod either by gluing, or bybrazing, the integration of this rod in a thermal and electricalcircuit, two examples of implementation of such elements for a device ofrefrigeration and for a microgenerator, and finally, a process ofrealization of such rods minimizing the cut and manipulation operations.

An assembly of rods constitutes a block whose applications are similar.

The rod presents as announced

an optimization of the electrical impedance, consequence of theoptimization of H/L2 and of the number of bars.

an optimization of the thermal impedance: The rod comprises anelementary thermal conductivity, the very simple association of the barsin series electrically and parallel thermally allows the matching of thethermal resistance of the rods to that of the associated preexistingthermal drains and dissipators.

a mechanical resistance improved by the fact of the composite structure.

a resistance to the corrosion improved by the fact that each element istotally coated in either resin, or nickel.

a simplification of the mounting, by the implementation of technicssimilar to those used in CMS.

The process of realization is optimized in term of cost by the fact thatit suppress the following elements:

individual bars cutting

handling individual bars

brazing on ceramic support

the mounting is less expensive, because it is limited to a hot gluing orto a brazing on printed circuit with dissipative support.

What is claimed is:
 1. A thermoelectric component of bismuth telluriumdoped with antimony and bismuth tellurium doped with selenium,comprising parallelepipedic bars of thermoelectric material which arejoined to one another (221, 222), coated on their faces opposite to anelectrically and thermally insulating membrane (223); mechanicallystrengthened on their flanks by an electrical and thermal insulatingmembrane (224), and covered on their apparent faces (225) with a thinelectrical circuit, to insure the electrical series connection of thebars.
 2. A thermoelectric component according to claim 1 comprised of arow of alternately P and N doped bars configured as rod, glued one onthe other on opposite faces by a membrane for fusible printing forinterlining, embedded by a lateral strengthened membrane, nickel-platedon the apparent faces of the bars, then brazed to an elementary thincircuit insuring the junction of a bar with an adjacent bar.
 3. Athermoelectric component according to claim 1 configured as aparallelepipedic module constituted by the juxtaposition of severalelementary components electrically connected in series and crossed inparallel by the thermal flow.
 4. A thermoelectric component of claim 1in combination with a generator of cold temperatures comprising analuminum plate covered with a thin electrical circuit insuring theconnection between components, components being fusion printed forinterlining to the plate or brazed and the components being covered byseveral dissipaters under an air flow driven by a ventilator.
 5. Athermoelectric component of claim 1 in combination with thermoelectricsgenerator which comprises components inserted between a collector at aselected temperature (281) and a dissipater at a different temperature(285), an electrical connection circuit being disposed between thecomponents (282).
 6. A process of realization of the component accordingto claim 1, characterized in that the original materials, in the form oftwo bars, one doped with selenium, the other with antimony, undergo afirst cycle of cutting in slices, then a reconstitution of the bar withinterleaving of membranes for fusible printing for interlining, withalternation of the materials form one slice to the other, then ahardening of the reconstituted bar, then a cutting in slice in aperpendicular plan, then a reconstitution with interleaving of membrane,and hardening, and finally a third cycle of cutting in the axisperpendicular to that of the bars, realizing components withoutelectrical circuit.
 7. A thermoelectric component of claim 1 incombination with a voltage generator for feeding a thermometer measuringthe temperature of a culinary container comprising at least athermocouple in iron disilicide or a thermocouple module one or theother of which are inserted between a sleeve and a container and isconnected to a converter circuit.
 8. Voltage generator for feeding athermometer measuring the temperature of a culinary container,characterized in that it comprises at least a thermoelectric couple iniron disilicide or a thermocouple module according to claim 1, one orthe other being inserted between the sleeve and the container, andconnected to a converter circuit which boosts the voltage provided by asource (1; 21) at low direct voltage with a small internal resistance(2), comprising a self-oscillating circuit, functioning at a very lowvoltage, using a voltage step-up transformer (3, 4, 6, 6′, 7; 20, 23,24, 20′, 23′, 24′) generating the control signals of two chopper-step-uptransformers (11-14; 25′-28″) with alternate operation, comprising anenhancement mode field effect transistor (11, 12; 25, 26, 25′, 25′)which is used as a synchronous switch with the self-oscillating circuit,which is connected in series with an inductance (13, 14; 27, 28, 27′,28′) to the terminals of said source (1,; 21) and which is connected tothe user circuit through a diode (15, 16; 29, 31, 29′, 31′).
 9. Athermoelectric component comprising: bismuth tellurium bars (222 and221) doped with antimony and bismuth tellurium bars doped with selenium,the bars providing a rod (220) made of alternating P and N doped bars(222 and 221), respectively; the bars (222 and 221) being joined to oneanother at opposing faces in a alternating array by electrically andthermally insulating membranes (223); the bars being mechanicallystrengthened along at least one set of coextensive side faces by anelectrically and thermally insulating membrane (224), and the barshaving nickel plated apparent faces (225) that have bismuth tin platedmembranes (263) that form a brazed connection with engraved coppernickel plated tracks (262) insuring junction of adjacent bars (222 and221), the engraved copper nickel plated tracks (262) being bonded to athin electrical circuit (261) realized from a thin epoxy glass membrane(264) loaded with boron nitride.
 10. A thermoelectric component made ofbismuth tellurium bars (222 and 221) doped with antimony and bismuthtellurium bars doped with selenium, to provide a rod (220) made ofalternating P and N doped bars (222 and 221) respectively; the bars (222and 221) being joined to one another at opposing faces in a alternatingarray by electrically and thermally insulating membranes (223); the barsbeing mechanically strengthened along at least one set of coextensiveside faces by an electrically and thermally insulating membrane (224),the bars having nickel plated apparent faces (225) that have bismuth tinplated membranes (263) that form a brazed connection with engravedcopper nickel plated tracks (262) insuring junction of adjacent bars(222 and 221); and the electrically insulating and thermally conductingmembrane (252, 264) being made of a copper engraved nickel-plated andbismuth tin plated material and the electrical circuit being realized ona rigid thermally conducting support (251, 265) covered with theelectrically insulating and conducting membrane (252, 264).
 11. Athermoelectric component, comprising: first parallelepipedic bars ofbismuth tellerium doped with antimony to provide a P material; secondparallelepipedic bars of bismuth tellurium doped with selenium toprovide an N material; an electricallly insulating, thermoplastic filmdisposed between opposed facing surfaces of the bars and adhered by heatto the opposed surfaces to join the bars together at the opposed facesthereof; the film being relatively thin and having relatively lowthermal insulation properties to facilitate heat transfer betweenadjacent bars; electrically insulating membranes extending transverse tothe films adhered to first adjacent, non-facing surfaces of the bars tomechanically strengthen the rod and to hold the bars in alignment, theelectrically insulating membranes being relatively thin, and a thinelectrical conductor adhered to second adjacent non-facing surfaces ofthe bars for providing a series electrical connection between the bars.12. The thermoelectric component of claim 11, wherein the film is madeof a polyflouride material.
 13. The thermoelectric component of claim 11wherein the total thickness of the film material between opposed facingsurfaces is in the range of 25 to 75 microns.